The present invention relates generally to aircraft propulsion, and more specifically to aircraft engines incorporating an open rotor for propulsion.
It is well-known to provide aircraft propulsion using open rotors, defined generally as an apparatus including a rotatable hub carrying an array of airfoils which are configured to produce thrust, and which are not surrounded by an outer shroud.
One type of open rotor is a conventional propeller. These are mainly used for low-speed applications and generally become inefficient at high subsonic speeds.
There is an interest in using open rotors to propel higher-speed vehicles using blades optimized therefor; these types of open rotor are often referred to as “prop fans” or “unducted fans”. In high-speed subsonic flight, the combination of rotor rotational speed, blade radius, and flight speed results in blade relative speeds that are supersonic through surrounding air, particularly at the outer span.
One problem with such open rotors is that blade-generated shock waves will propagate outward from the rotor and impact the aircraft fuselage, producing vibration and cabin noise. Since blade-generated cabin noise is an obstacle to future acceptance of the open rotor engine architecture for commercial aircraft propulsion systems, it is desirable that it be minimized.